Who followed my mining adventure knows, that I almost gave it up, because I couldn't mine at a profit.

I pay 0.27 EURO the kWh and it's really hard to compete then.

Especially with a R9 280X.

I tried several times to undervolt my GPU (including BIOS flash), but AMD's Crimson tool or Claymore miner itself (I never figured that out) kept overwriting my settings instantly.

Yesterday I spent some more hours testing different driver versions and settings.

After uninstalling Crimson and installing AMD Minimal Setup and then MSI Afterburner and going through different threads to figure out how to unlock the Core Voltage in AMD Afterburner, I finally found the solution.

This is a Gigabyte R9 280X Windforce ( 100 Euros second hand )

I went down from:

1.2 Volts core voltage
1100 Mhz core clock
1500 Mhz memory clock

to:

0.97 Volts
950 Mhz core clock
1250 memory clock

The default settings resulted in ~270 Watt off the wall:

I could bring it down to ~140 Watt off the wall:

That's almost half !

Meanwhile, Hashrates dropped from ~290 Sol/s (or H/s) to ~270 Sol/s.

In other words:

Energy intake reduced by ~50%; hashrate only dropped by less than 10%.

If I reduce the memory clock more, I will lose hashrates significantly.
If I reduce the core clock more, I will also lose hashrates significantly.
If I reduce the core voltage more, the GPU driver will crash (nasty).

I could try to reduce the memory voltage, but for that I'd have to do BIOS flashing again and the testing takes much longer. AMD Afterburner doesn't have that feature. The features it has, are fine for now.